Can Your Robot Handle the Heat?

July 2015
By Bryan Bergeron

I’m working with a team of engineers on a DOD-sponsored project to develop a physiologically accurate robot the size and shape of an adult male. As you might expect, there are a number of challenges such as how to pump fluid “blood” from the torso to the arms and legs while maintaining a physiologically accurate pulse, as well as how to provide a realistic sucking wound in a scenario where the chest is penetrated with a piece of shrapnel from an IED. There are dozens of servos, solenoids, microcontrollers, pumps, and hundreds of sensors in the design.

One of the many things that this project has taught me is to appreciate the difficulty of dissipating heat in a close space. On a drone, you have the luxury of air flowing over heatsinks on a microcontroller board to provide convection cooling. On a submersible, there’s typically the heatsink of flowing water on the thermally conductive hull. I’m not sure exactly how NASA engineers deal with heat buildup in closed airless satellite systems, but I’m impressed that they’ve found a way to dissipate the heat generated by all those components.

So, picture a human sized chassis, covered with thermally insulating “skin,” with the batteries typically supplying 12 VDC in excess of 20A. That’s about twice the power required by an Easy Bake Oven. Now, I’ll concede that a 120W light bulb is less efficient than a microcontroller or a solenoid, but there is still a great deal of heat to deal with. Poking a few holes in the chest wall and inserting a fan isn’t an option because the fan noise would interfere with normal breath and heart sounds (as heard by a stethoscope). Using the blood system is potentially problematic in that failure of the circulatory system could result in a spike in heat buildup and catastrophic failure of the robot.

If you’re familiar with the Hondo Asimo, you’ve seen one answer to the heat problem: simply install a backpack air conditioner on the robot. That’s not a option in our case, as we’re limited to anatomically correct design. We haven’t licked the problem yet, but we’re getting there.

The point of this editorial is to suggest that you think about the scalability of your robot designs — especially when it comes to heat dissipation. I never considered heat with small carpet roamers or even larger crawlers, where the servos are exposed to the elements. However, when you start hardening a design, protecting it from the elements, you’re also probably interrupting the routes of heat dissipation. Because catastrophic thermal runaway can be expensive, heat dissipation is worth considering in your next large-scale robot design. SV